"We got the biggest mandate," said the leader of the National Coalition Party, after a dramatic night in which the result gradually swung away from Ms Marin's Social Democrats.

Mr Orpo secured 20.8% of the vote, ahead of the right-wing populist Finns Party and the centre left.

The populists won a record 20.1%.

It is a bitter defeat for Ms Marin, who increased her party's seats and secured 19.9% of the vote.

She continues to enjoy high poll ratings and has been widely praised for steering Finland towards imminent entry into Nato and navigating her country through the Covid-19 pandemic.

Shortly after the conservative leader claimed victory, the centre-left leader conceded the election.

"Congratulations to the winner of the elections, congratulations to the National Coalition Party, congratulations to the Finns Party. Democracy has spoken," she told supporters.

For weeks the three parties had been almost level in the polls, and as the results came in it became too close to call. Then a projection from public broadcaster YLE gave Petteri Orpo's National Coalition victory with the biggest number of seats in parliament.

"I think Finnish people want change. They want change and now I will start negotiations, open negotiations with all parties," he said.

There was a mood of euphoria in the camp, said Matti Koivisto, political correspondent with public broadcaster YLE. "When they saw the projection, it was quite clear they were going to win."

Finns Party leader Riikka Purra congratulated her centre-right rival and was herself delighted with the best result in her party's history.

"We're still challenging to be number one, but seven more seats is an excellent result."

The Finns underlined their success by winning more regions than any other party in mainland Finland. Riikka Purra won more votes than any other candidate and commentators highlighted her party's appeal to young voters by reaching out over social media such as TikTok.

Riikka Purra celebrated her party's record electoral success

Meanwhile, three of the other parties in the outgoing coalition - the Centre Party, Left Alliance and Greens - all rang up big losses.

Now 37, Sanna Marin became the world's youngest leader when she burst on to the political scene in 2019. She headed a coalition of five parties, all led by women.

Despite her successful response to neighbouring Russia's invasion of Ukraine, the election was largely fought on Finland's economy and public debt as all the mainstream parties backed Nato membership. Finland officially becomes Nato's 31st member on Tuesday.

Many Finns see Ms Marin as a polarising figure. She came under heavy scrutiny last year when a video emerged of her singing, dancing and drinking at a party. Supporters said the controversy was steeped in sexism and women across Finland and the world shared videos of themselves dancing in solidarity.

Petteri Orpo by contrast has none of Sanna Marin's "rock-star" qualities, says YLE's Matti Koivisto.

"He's a career politician. He's been in the game since the 1990s and he's quite stable and calm. There is criticism that maybe he's too dull and calm, but it also works quite well in Finland."

The conservatives will have the first opportunity in forming a government, and if they succeed, Mr Orpo, 53, will become the next prime minister.

Under an Orpo-led government, Europe could expect a pro-European conservative from the liberal centre of his party with an emphasis on economic policy.

Less exciting than Sanna Marin and very moderate, says Vesa Vares, professor of contemporary history at the University of Turku: "A sort of dream son-in-law."

Under Finland's system of proportional representation he will have to muster more than 100 seats in the 200-seat parliament to run the country, and that will not be straightforward.

Mr Orpo really has two choices ahead of him, either forming a right-wing coalition with Riikka Purra's nationalist Finns Party or reaching an agreement with Sanna Marin's Social Democrats.

"The Finns are a very difficult partner because they're so inexperienced and they have MPs who are discontented towards almost anything," says Prof Vares.

"The most natural thing would be to co-operate with the Social Democrats. But [Sanna Marin] used to belong to her party's left wing and it's obvious she doesn't like the conservatives."

Politics researcher Jenni Karimaki of the University of Helsinki also points out that Ms Marin has been reluctant to say what her aspirations are.

The Social Democrats have mixed feelings, she says, because while they increased their seats in parliament, they were unable to become the biggest party and renew their premiership.

"But Finnish political culture is known for its flexibility. They are known for their ability to negotiate and form compromises."